1. Field of the Invention
The present invention relates to a foamed synthetic fiber and its manufacturing method and more particularly to a novel and useful fiber which, provided with the known features of foamed fiber, has its most serious defect of low strength improved and also feature its improved feeling and development of color like animal hairs.
2. Description of the Prior Art
Besides the so-called essential improvement of fiber and its functions through designing of new textile composition and impartation of textile properties, various measures have been taken in recent years for improvement of their added values through contrivance of the fiber's three-dimensional structure. So, among others, effort has been made for further subdivision of the so-called islands type of fiber's cross-section such as seen in animal hairs, and reforming attempts have been made through adoption of profile cross-sections and further improvement of the fiber's fine surface. The foamed fiber belongs to the latter category and various attempts have been made for forming inside the fiber isolated or mutually continuous bubbles or a combination thereof for improved lightweight feature, bulkiness, soft touch, elasticity etc.
As typical examples are cited in Japanese Patent Publication No. 4536/68, Japanese Patent Publication No. 850/71 and Japanese Laid Open Patent Application No. 36208/83. These, however, invariably deal with synthetic rush and industrial materials or interior decoration materials, not dealing with the so-called general fibers including those for clothing. Worse, the materials proposed with their construction lack in mechanical properties required for spinning, weaving and knitting etc. ordinary fibers are to undergo, in mechanical strength and elongation in particular, and still more serious is their poor dyeability (behavior in dope dyeing, dyeing or printing), the colored products badly lacking in gloss and transparency. Meanwhile, Japanese Patent Publication No. 21300/67, Japanese Patent Publication No. 210/76, Japanese Patent Publication No. 38527/83 etc. are supposed to be intended for use in this field, but the fiber constructions proposed in these inventions have only a few bubbles per fiber cross-section, thus being insufficient for the feature of foamed fiber to be fully exhibited.
Further, Japanese Laid Open Patent Application No. 77616/75 discloses a conjugated fiber but it can hardly be economically advantageous for
(1) sheath and core cannot be made of the same composition;
(2) more than one kind of dope are required; and
(3) complicated equipment is required for its manufacture because of, among others, compound nozzle required; and
(4) the performance is largely different from what is aimed at by the present invention.